With great advance of battery and semiconductor technologies, so many kinds of handheld apparatuses, such as mobile phones, portable multimedia players (PMPs), remote controls, MPS players, personal digital assistants, digital cameras, portable global positioning systems, electronic dictionaries, the SideShow devices used for the VISTA operating system of Microsoft etc., become popular. It is very confused and inconvenient that a user carries or uses various individual handheld apparatuses. Thus, a 2-in-1 integrating approach is adopted by many conventional handheld apparatuses, such as a combination of a SideShow device and a remote control, or a combination of a mobile phone and a PMP. Usually, those 2-in-1 apparatuses arrange keypads of the two combined systems on two opposite side of a cuboidal housing, respectively. When a user holds the 2-in-1 apparatus with his/her palm to operate either of the two systems facing him/her, it will be very possible that the keypad on backward side of another system not being operated is unintentionally pressed. Therefore, undesired operations and unnecessary power consuming of battery will occur.
It is necessary for those handheld apparatuses with double-sided keypad arrangement that they equip a switch for switching a keypad on either side to be enabled and the other one to be disabled because the switch can prevent users from intentional operations to the disabled keypad. The abovementioned switches may adopt either manual or automatic manner. The manual manner is to be executed by a manual operation applying on a mechanical switch. It is inconvenient. The automatic manner uses a gravity sensor to detect the directionality of the handheld apparatus for judging one-sided keypad is in an upward direction. The judged upward keypad belongs to the system the user is using. Therefore, that keypad is automatically enabled, and the other one is disabled simultaneously. However, all the conventional methods for judging directionality by utilizing a gravity sensor have to make an accurate and complicated calculation for component quantities on three dimensional rectangular coordinate axes to obtain a judging result. Such calculations require microprocessors with high performance to execute. Those microprocessors are not only larger in size also expensive in cost, so that they are not suitable for small-scale apparatuses or low-price products.